Journal of Neuroscience, Vol 8, 4334-4339, Copyright © 1988 by Society for Neuroscience
Do the relative mapping densities of the magno- and parvocellular systems vary with eccentricity?
MS Livingstone and DH Hubel
Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115.
Two recent papers on the macaque visual system have concluded that in the
lateral geniculate body the ratio of the number of cells in the
magnocellular system to the number in the parvocellular system representing
the same area of visual field increases by a factor of 20 between the fovea
and the far periphery. In the primary visual cortex the relative cell
densities of the 2 systems change little with eccentricity. These
calculations therefore predict a 20-fold change in the relative densities
of the inputs to the visual cortex from the 2 subdivisions of the lateral
geniculate body. To test this prediction, we asked if the following vary
with eccentricity: (1) the ratio of the number of magnocellular to
parvocellular neurons innervating a given area of striate cortex and (2)
the relative density, in the magno- and parvo-recipient sublaminae of layer
4C, of radioactivity transported from the eye to the cortex. Neither of
these ratios showed any significant variation with eccentricity. These
results seem to throw doubt on the contention that the ratio between the
magnocellular and parvocellular layers of the number of cells per degree2
of visual field varies significantly with eccentricity.